154 CALIFORNIA ACADEMY OF SCIENCES. 



Externally tliis species nuich resembles a Kel/ia, l>iil may lie (listiiii;iiislu(l hy 

 till- pallial sinus ami hinge teeth. Specimens idcntilit'd liy Di. Dull. 



Two left valves from lower 8an Pedro series of Deathuan Island, one (tf which 

 is lli^nred, and is now in the collection of Delos vVniold. Rather eoniiudn in the 

 Pleistocene at Spanish Bii;ht, San Diej^o. 



Living. — Vancouver Island to Todos Santos Bay (Dall). 



Pleistocene. — San Pedro (Dall; Arnold): San Diego (Arnold). 



Family XXIX. I'ETRICOLlD.lv 



(iiMius Petricola lAuaarck. 



Shell oval or elongated, lliiii, Uuiiul, anterior side short; hinge with generally three teeth in 

 each valve, the e.xternal often obsolete; pallial .sinii.s deep. 



Type, Venns lapicida (Chemii.). 



Section Petricola Lamarck h. s. 



Shell ovate, with a short or moderately wide jjallial sinus, the radial scul[)ture more or less 

 divaricate or zigzag. 



Type, Petricola lapicida (Gmel.). 



94. Petricola carditoides ('onrad. 



Saxkava carditoides Con., Jour. Acad. Nat. Sci. Phil., Vol. VII, 1837, p. 255, PI. XX, fig. 8. 



Petricola carditoides CoN., Jour. Acad. Nat. Sci. Phil., 1849, p. 213. Carpenter, Proc. Zool. Soc, 

 1856, p. 214; =P. californica CoN. =/*. cylindracea Desh. =/'. arcuaia Desh. ^P. 

 gibba MiDD. (yfa^i' Carpenter, Brit. Assn. Rejjt., 1863, p. 641). Cooper, 7th Ann. 

 Rept. Cal. St. Min., 1888, p. 258. Keep, West Coast Shells, p. 183, 1892. William- 

 son, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 189. Dall, Trans. Wagner Inst. Sci., 

 Vol. Ill, Part 4, 1898, p. 835; Part 5, 1900, p. 1059. 



Shell of medium size and variable outline, generally oblong-oval, conve.x, thick; surface 

 ornamented with fine, concentric, incremental lines, which sometimes form irregular ridges, and by 

 fine, wavy, radiating lines; hinge-area prominent; three cardinal teeth in each valve, the anterior one 

 smallest; margin smooth. 



Dimensions.— X.on^. 28 mm.; alt. 25 mm.; diam. 16 mm. 



A variable form which is recognized, however, by its sciil[)tnre, prominent 

 teeth and thick shell. Often found in holes in the pebbles and boulders comprising 

 the conglomerate in this formation. Specimens identified by Dr. Dall. 



Not uncommon in the lower San Pedro series at Deadman Island; and in 

 the upper San Pedro series at Deadman Island, Los Cerritos, Crawfish George's, and 

 San Pedro. Found also in the Pleistocene at Spanish Bight, San Diego. 



Living. — Sitka to San Diego (Cooper). 



Pleistocene. — San Pedro to San Diego (Cooper) : San Pedro; San Diego 

 (Arnold). 



